FR3087539A1 - MEASURING INSTRUMENT WITH MEASUREMENT SPOT VISUALIZATION SYSTEM AND VISUALIZATION ACCESSORY FOR SUCH MEASURING INSTRUMENT - Google Patents

Abstract

The invention relates to a measuring instrument (100) comprising an excitation section (1) emitting an incident light beam (12) at an oblique angle of incidence. According to the invention, the analysis section (2) of the measuring instrument (100) has an optical beam splitter (27) transmitting part of the measuring light beam (22) to an imaging system (28). ) adapted to acquire a first image (51) of the sample and in that the measuring instrument further comprises a second light source (41) emitting an illumination beam (42) at near-normal incidence and a second imaging system (46) adapted to acquire a second image (52) of the sample and an image processing system (5) adapted to extract an image from the measurement spot of the first image (51) and to forming a third image (58) comprising a projection (57) of the image of the measurement spot, resized and arranged in superposition in the second image (52).

Description

TECHNICAL FIELD TO WHICH THE INVENTION RELATES The present invention relates generally to the field of scientific measuring instruments intended for the analysis or measurement of samples by reflection or transmission of a light beam.

It relates more particularly to instruments for measuring or analyzing materials based on the effects of polarization of light as a function of a variable angle of incidence such as, for example, a polarimeter or an ellipsometer or reflectometer.

It relates in particular to a sample display system for an ellipsometer or polarimeter or a reflectometer with a variable angle of incidence.

TECHNOLOGICAL BACKGROUND Throughout the description, the same elements are identified by identical reference signs.

An ellipsometer or polarimeter is a measuring instrument that uses polarized light to measure the dielectric properties of an isotropic or anisotropic sample, in order to deduce its physicochemical structure or composition.

The most common application of an ellipsometer is the analysis of very thin films such as layers on semiconductor wafers or glass substrates.

An ellipsometer or a polarimeter can be used in situ to monitor the deposition or etching of thin films.

The most common configuration for an ellipsometer or polarimeter is a reflective configuration with an angle of incidence oblique to the normal to the surface of a sample to be analyzed.

However, there are also ellipsometers or polarimeters operating in transmission with an oblique angle of incidence.

There are also variable angle of incidence instruments, which allow the angle of incidence to be adjusted as a function of the sample or to measure the ellipsometric or polarimetric properties as a function of a varying angle of incidence within a range. angular range determined.

FIG. 1 schematically shows a side view of an ellipsometer as disclosed in patent document WO2008 / 087217.

This ellipsometer comprises an excitation section 1 including a light source 11 and a polarizing device 14 and an analysis section 2 comprising a polarization state analyzer 2 24 and a detection system 26 of the ellipsometric signal.

The polarizing device 14 generally comprises a polarizer and / or an optical polarization modulator.

Thus, the excitation section 1 emits a polarized incident measuring light beam 12 propagating along an optical axis 13 towards the surface 30 of the sample 3.

The optical axis 13 of the incident measuring light beam 12 forms an angle of incidence, denoted A01, with the normal 31 to the surface 30 of the sample 3.

Also shown in Figure 1, an orthonormal frame XYZ, in which the Z axis is parallel to the normal 31 and the optical axis 13 of the incident measuring light beam 12 is in the XZ plane, also called the plane of impact.

Advantageously, the excitation section 1 comprises an optical focusing system 15 for focusing the incident measuring light beam 12 into a measuring spot 32.

The measurement spot is generally formed by focusing the image of a source hole projected onto the surface of the sample.

From a circular source hole, one generally obtains a measuring spot of elliptical shape because of the oblique angle of incidence.

The analysis section 2 is arranged to receive a measuring light beam 22 formed by reflection (or transmission) of the incident measuring light beam 12 on the sample.

In a reflection configuration, the measurement light beam 22 propagates along an optical axis 23 forming a symmetrical angle, denoted -A0I, of the angle of incidence with the normal 31 to the sample.

Generally, the analysis section 2 includes another optical system 25 for forming the image of the measurement spot on the detection system 26 of the ellipsometric signal.

The detection system 26 comprises at least one optoelectronic detector adapted to receive the measurement light beam 22 and to record at least one ellipsometric or polarimetric signal as a function of the state of polarization of the polarizing device 14 and of the analyzer. polarization state 24.

The optoelectronic detector can be a single-channel detector, for example a photomultiplier (or PMT) or a solid near infrared (NIR) detector, for example in InGaAs, or a linear array of pixels at one dimension (1D) or a matrix of pixels at two-dimensional (2D), for example a CCD or CMOS camera.

In some embodiments, the detection system 26 includes a monochromator or spectrometer with a one-dimensional (1D) or two-dimensional (2D) detector for spectroscopic measurements.

This 3 ellipsometer further comprises a display system 8 arranged near the normal 31 to the surface 30 of the sample 3 to collect a light beam 19 diffused by the sample.

However, such a viewing system 8 only allows viewing of the measurement spot 32 on a scattering sample.

5 However, most of the samples are not scattering.

It is desirable to visualize the position of the measurement spot on any type of sample, scattering or non-scattering, and in particular in the case of a spatially non-uniform sample, for example patterned.

This is because a small spot size (from 10 micrometers to a few hundred microns) is used to analyze 10 small areas of the sample, in particular small areas on a sample with microscopic patterns, such as an integrated circuit. (IC) or a flat screen (FPD for flat panel display in English terminology).

In such applications, it is necessary to precisely position the spot relative to the surface of the patterned sample for proper analysis.

However, the low intensity of the scattering of the measurement spot received by a viewing system 6 arranged along the normal to the surface of the sample makes this positioning task relatively difficult.

FIG. 2 illustrates another ellipsometer comprising another display system as disclosed in patent document WO 2008/087217 A1.

In Figures 1 and 2, the same reference signs denote analogous or similar elements.

In the ellipsometer of FIG. 2, the excitation section 1 further comprises an auxiliary light source 16 emitting a viewing beam 18 and a semi-transparent plate 17 which combines the viewing beam 18 with the measurement light beam. incident 12 polarized so that they propagate along the same optical axis 13.

The viewing beam 18 illuminates an area 38 around the measurement spot 32, the illuminated area 38 being larger than the measurement spot 32.

By reflection or transmission of the viewing beam 18 on the sample, a reflected viewing beam 21 is obtained (or transmitted) propagating along the same optical axis 30 23 as the reflected measuring light beam 22 (or transmitted) in the direction of analysis section 2.

On the other hand, the analysis section 2 comprises an optical beam splitter 27, generally a retractable mirror, adapted to simultaneously transmit a part 121 of the reflected viewing light beam 21 and a part 122 of the reflected or transmitted measurement beam 22. in the direction of a viewing device 123, comprising for example an eyepiece or a camera.

In the example of FIG. 2, the analysis section 2 comprises an opening 120 for the passage of the beams 121, 122 towards the display device.

Such a visualization system makes it possible to visualize simultaneously on the same image the measurement spot 32 and the zone 38 illuminated by the visualization beam 18 on a sample, whatever the angle of incidence.

In addition, the image of the measurement spot remains visible even on a non-scattering sample.

However, in the case where a camera 123 is used to form the image of the sample and the measurement spot, the image is generally distorted (blurred) due to an angle between the surface of the sample and the measurement spot. a plane optically conjugated with the plane of the camera.

In addition, the superposition of the optical path of the viewing light illumination beam with that of the measurement light beam is liable to disturb the ellipsometric measurement, so that the visualization and the measurement are generally carried out sequentially and not simultaneously.

It is desirable to provide a viewing system for a measuring instrument based on an oblique incident light beam, of the ellipsometer or polarimeter or reflectometer type, in particular with a variable angle of incidence, which makes it possible to visualize in real time during the ellipsometric measurement. or polarimetric or reflectometric and with sharpness over the entire field of view: a spot incident on a sample and the surface of the sample around the measurement spot, whether the surface of the sample is scattering or non-scattering.

It is desirable to provide a viewing system for an ellipsometer or polarimeter or reflectometer which allows precise positioning of the measurement spot relative to a pattern on the surface of the sample.

In particular, it is desirable to provide a viewing system for an ellipsometer making it possible to clearly visualize the measurement spot and the surface of the sample around the measurement spot whatever the angle of incidence, this visualization system being able to be operational simultaneously with ellipsometric measurements without disturbing ellipsometric measurements.

Moreover, in most previous viewing systems, when the sample is transparent, for example on a thin glass substrate with flat and parallel faces, multiple reflections are observed, forming at least two spots, by reflection between the face. front and back side of the substrate.

It is sometimes difficult to differentiate the useful spot for measurement from the parasitic spot (s) resulting from multiple reflections.

These multiple reflections can therefore be troublesome to precisely position the measurement spot on a sample.

It is therefore desirable to provide a viewing system for a measuring instrument based on an oblique incident light beam, of the ellipsometer or polarimeter or reflectometer type, making it possible to view an incident spot on a sample while discriminating the other spots formed by multiple reflections. .

Finally, it is desirable to upgrade an old ellipsometer or polarimeter or reflectometer to incorporate a visualization system to improve both the visualization of the measurement spot and of the sample area around the measurement spot. .

OBJECT OF THE INVENTION In order to remedy the aforementioned drawbacks of the state of the art, the present invention proposes a measuring instrument comprising an excitation section and an analysis section, the excitation section including a first source. of light adapted to emit an incident light beam for forming a measurement spot on a sample at an oblique angle of incidence, the analysis section being arranged to receive a measurement light beam formed by reflection or transmission of the light beam incident on the sample, the analysis section comprising a detection system adapted to detect a part of the measurement light beam.

More particularly, according to the invention there is provided a measuring instrument in which the analysis section comprises a first optical beam splitter and a first imaging system, the first optical beam splitter being arranged on an optical path of the beam. light measurement and capable of transmitting another part of the measurement light beam to the first imaging system, the first imaging system being adapted to acquire a first image of a first zone of the sample around the spot 30 of measurement, the measuring instrument further comprising a second light source arranged so as to emit an illumination beam intended to illuminate at almost normal incidence a second zone of the sample around the measuring spot, a second system of 'imaging arranged to receive an imaging light beam formed by reflection of the illumination beam 6 on the second area of the sample and acquire a second i image of the second area of the sample and an image processing system adapted to receive the first image and the second image, the image processing system being adapted to extract an image from the measurement spot of the first image and to form a third image comprising a projection of the image of the measurement spot, the projection being resized according to the angle of incidence of the incident light beam and said projection being positioned and arranged in superposition or in incrustation in the second image of the second area of the sample.

The illumination beam at normal incidence provides uniform illumination of the sample surface.

Imaging from a reflected beam at normal incidence reduces image distortions of the sample via the second imaging system because the sample is thus located in an optically conjugated plane of the second imaging system. imagery.

The combination of this uniform illumination and the image formation of the sample without distortion helps to greatly improve the image quality of the sample throughout the area that one wishes to view around the measurement spot, whatever the type of sample, scattering or non-scattering, with or without a pattern and regardless of the angle of incidence of the ellipsometry or polarimetry measurement.

In addition, image processing and merging of the first image and the second image into a single image, the third image, allows a crisp and precise visualization of the position and extent of the measurement spot on the surface. of the sample, depending on the angle of incidence of the measurement beam on the sample.

The invention thus makes it possible to visualize an incident spot of ellipsometric or polarimetric or reflectometric measurement on a sample, including on a non-scattering sample.

The invention simultaneously provides a clear image without distortion of an area of the sample around the measurement spot, regardless of the angle of incidence.

The visualization system makes the use of a measuring instrument easier, the visualization being able to be updated in real time and carried out during a measurement.

In addition, image processing can be automated for industrial applications.

Other non-limiting and advantageous characteristics of the measuring instrument according to the invention, taken individually or according to all the 7 technically possible combinations, are as follows: the measuring instrument further comprises a second optical beam splitter arranged to receive the illumination beam from the second light source and direct the illumination beam to the sample, and the second optical beam splitter being adapted to receive the imaging light beam and to direct it to the sample. direct to the second imaging system; the measuring instrument comprises at least one polarizing optical device arranged on an optical path of the illumination beam and / or of the imaging light beam; the second imaging system comprises a camera, an objective and a spatial filter arranged in an object focal plane of the objective, the spatial filter being adapted to reduce optical aberrations on the second image; the image processing system comprises an image recognition subsystem suitable for delimiting an outline of the image of the measurement spot in the first image and / or for determining a first position and a first orientation of the first area of the sample in the first image and / or, respectively, to determine a second position and a second orientation of the second area of the sample in the second image; the image recognition subsystem is adapted to automatically recognize at least one pattern in the second image; the image recognition subsystem is suitable for recognizing and selecting the image of the measurement spot from among a plurality of images formed by multiple reflection between two faces of the sample; the measuring instrument further comprises a third optical beam splitter and another detection system, the third optical beam splitter being arranged on the optical axis of the illumination beam, the third optical beam splitter being adapted to transmitting a portion of the light beam formed by reflection of the illumination beam on the second area of the sample to the other detection system, the other detection system being adapted to provide a signal representative of an angle between the normal to the surface of the sample and an optical axis of the illumination beam; - the measuring instrument comprises a sample holder fitted with an actuator system adapted to modify at least one angle of inclination of the sample holder transversely to the normal to the surface of the sample and a suitable electronic system to receive the signal representative of the angle between the normal to the surface of the sample and the optical axis of the illumination beam 5 (42) and to apply a command to the actuator system; - The analysis section comprises a polarization state analyzer arranged on an optical path of the measuring light beam and the detection system is adapted to detect an ellipsometric or polarimetric signal.

The invention also provides a viewing accessory for a measuring instrument based on the emission of an incident light beam intended to form a measurement spot on a sample at an oblique angle of incidence and the detection of a light beam. measuring device formed by reflection or transmission of the light beam incident on the sample, the measuring instrument comprising a first imaging system adapted to generate a first image of a first zone of the sample around the measuring spot, the first image being formed by reflection or transmission of the light beam incident on the sample.

According to the invention, the viewing accessory comprises a second light source and a second imaging system, the second light source being arranged so as to emit an illumination beam intended to illuminate a near-normal incidence. second zone of the sample around the measurement spot, the second imaging system being arranged so as to form a second image of the second zone of the sample by reflection of the illumination beam on the second zone of the sample and an image processing system adapted to receive the first image and the second image, the image processing system being adapted to extract an image from the measuring spot of the first image and to form a third image comprising a projection of the image of the measurement spot superimposed or inlaid with the second image of the sample, the projection being resized as a function of the angle of incidence of the light beam i incident.

According to a particular and advantageous aspect, the viewing accessory comprises a third optical beam splitter and another detection system, the third optical beam splitter being arranged on the optical axis of the illumination beam, the third optical beam splitter. beam 9 being adapted to transmit a portion of the light beam formed by reflection of the illumination beam on the second zone of the sample to the other detection system, the other detection system being adapted to supply a signal representative of an angle between the normal to the surface of the sample and an optical axis of the illumination beam.

DETAILED DESCRIPTION OF AN EXAMPLE OF EMBODIMENT The description which will follow with reference to the appended drawings, given by way of nonlimiting examples, will make it clear what the invention consists of and how it can be implemented.

In the accompanying drawings: - Figure 1 shows schematically in side view an ellipsometer provided with a first display system according to the prior art; - Figure 2 shows schematically in side view another ellipsometer provided with another display system according to the prior art; FIG. 3 illustrates a display image of a sample and of a measurement spot obtained with a display system according to the principle illustrated in FIG. 2; - Figure 4 shows schematically in side view an ellipsometer according to one embodiment; FIG. 5 illustrates an example of a first measurement spot image obtained under oblique incidence with a first imaging system disposed in the analysis section of the ellipsometer; FIG. 6 illustrates an example of a second image of the surface of the sample obtained with a second imaging system arranged at normal incidence; FIG. 7 illustrates an image processing step applied to the first image (obtained in FIG. 5) in order to extract therefrom an image of the measurement spot, - FIG. 8 represents the image of the measurement spot extracted from FIG. 7 ; FIG. 9 illustrates another image processing step applied to the image of the measurement spot of FIG. 8 in order to cut out the useful surface, of the image, where the measurement spot is focused; FIG. 10 illustrates a projection and / or scaling step applied to the image of the contour of the measurement spot of FIG. 9 in order to deduce therefrom a projection of the image of the measurement spot; FIG. 11 illustrates an example of a third image obtained by superposition or inlay or grafting of the projection of the image of the measurement spot (illustrated in FIG. 10) with the second image of the surface of the sample 5 in normal incidence; FIG. 12 diagrammatically represents an imaging subassembly at normal incidence according to a variant of the present disclosure; - Figure 13 shows schematically in perspective view of an ellipsometer with a variable angle of incidence mounted on a goniometer, according to a particular embodiment.

Device In this document, by normal or quasi-normal incidence is meant an angle of incidence less than or equal to 5 degrees, and preferably less than 1 degree or zero with respect to the normal to the surface of the sample at 15 the location of the measurement spot.

By oblique incidence is meant an angle of incidence greater than or equal to 5 degrees and preferably between 10 degrees and 90 degrees relative to the normal to the surface of the sample.

FIG. 3 illustrates an example of a visualization image of a sample and of a measurement spot obtained by a visualization system of an ellipsometer 20 as illustrated in FIG. 2 with an angle of incidence of approximately 70 degrees.

The image of the measurement spot 32 is clearly observed on the sample.

The sample here comprises patterns 39 of variable dimensions.

However, by moving in the image along the X axis, we see that the image is generally distorted (blurred) outside a small area.

The extent of the sharpness zone is highly dependent on the angle of incidence and the imaging optical system used.

The sample image quality is degraded by lack of sharpness over a large part of the image due to the 70 degree angle of incidence.

This low quality of the display image makes it difficult to position the measurement spot with respect to the patterns of the sample.

In addition, it is difficult to assess the actual dimensions of the measurement spot from such an image.

Thus, the measurement spot 32 is viewed by the camera in an approximately circular shape in the optical viewing axis (see FIG. 3), while its real shape on the sample is elliptical with a strong ellipticity.

FIG. 4 schematically shows an ellipsometer 100 11 according to an embodiment of the present disclosure.

The ellipsometer 100 has an excitation section 1 and an analysis section 2.

The excitation section 1 comprises a first light source 11 adapted to emit an incident light beam 12 propagating along an optical axis 13.

The first light source 11 can be a laser or an LED for monochromatic measurements or a multi-wavelength diode for polychromatic measurements or any other conventional white light source, fiber or lamp pumped by laser diodes for measurements 10. spectroscopic.

The excitation section 1 comprises a polarizing device 14.

Preferably, the excitation section 1 comprises an optical focusing system 15 with spherical lenses or mirrors for focusing the incident measuring light beam 12 into a measuring spot 32.

The oblique angle of incidence (A01) is generally between 10 degrees and 90 degrees.

It should be noted that the excitation section 1 does not include an auxiliary lighting source, unlike the system described in connection with FIG. 2.

The analysis section 2 is arranged to receive the measurement light beam 22 formed by reflection (or transmission) of the incident light beam 12 on the sample 3.

The analysis section 2 further comprises an optical beam splitter 27 disposed between the detection system 26 of the ellipsometric signal and a first imaging system 28.

The first imaging system 28 comprises an image detector 29, for example a pixel array camera.

The image detector 29 is for example a Videology 24C1.35USB camera having 1280 x 1024 pixels, connected by USB 2.0 cable to a USB card of the control computer.

The optical beam splitter 27 is chosen from a glass plate or UV plate without treatment or semi-transparent plate with dielectric coatings or splitter plate (polarized or not) or Polka-Dot splitter plate or splitter cube (polarization or not) or prisms or polarizer or filter (for example wavelength separator) or a retractable mirror.

The optical beam splitter 27 is adapted to transmit a part 222 of the reflected or transmitted measurement beam towards the first imaging system 28 and simultaneously another part 224 of the reflected or transmitted measurement beam towards the detection system 26 of the ellipsometric signal.

The image detector 29 of the first imaging system 28 thus acquires a first image 51 of the measurement spot 32 on the sample regardless of the angle of incidence of the measurement light beam on the sample.

Simultaneously, the detection system 26 can detect the other part 224 of the reflected or transmitted measurement beam 5 and record an ellipsometric signal corresponding to this measurement spot 32.

The ellipsometer of the present disclosure further comprises an imaging subassembly 4 at normal incidence.

This imaging sub-assembly 4 comprises a second light source 41 or auxiliary source, a second optical beam splitter 43 and a second imaging system 46.

The second light source 41 is for example a white electroluminescent diode (or LED) or a conventional lamp or a fiber source or a lamp pumped by a laser diode.

Advantageously, the second imaging system 46 comprises an image detector, for example a CCD camera.

The second light source 41 or auxiliary source emits an illumination beam 42.

Advantageously, an optical system 48 is placed in front of the auxiliary source 41 so as to collimate the illumination beam 42.

For example, the auxiliary source 41 is an LED and the optical system 48 consists of an aspherical lens or a collimator adapted to form the illumination beam 42 collimated.

The second optical beam splitter 43 is chosen from the following optical components: semi-transparent plate or splitter plate with dielectric coating (polarized or not) or Polka-Dot splitter plate or splitter cube (polarized or not) or prisms or polarizer or filter .

The second optical beam splitter 43 directs the illumination beam 42 towards an area of the sample around the measurement spot 32 along an optical axis preferably aligned with the normal 31 to the surface of the sample.

Thus, the illumination beam 42 illuminates at normal (or near-normal) incidence a second zone 34 of the sample around the measurement spot 32.

An imaging light beam 44 is formed by reflection of the illumination beam 42 on the sample.

The imaging light beam 44 propagates along the normal 31 to the surface of the sample in the opposite direction of the illumination beam 42.

The second optical beam splitter 43 directs the imaging light beam 44 to the second imaging system 46.

A multiple lens optical system or camera lens 45 forms the image of the second area 34 of the sample on the camera of the second imaging system 46.

The camera of the second imaging system 46 is for example a Videology 24C1.35USB color camera comprising 1280 × 2014 pixels and connected by USB 2.0 cable to another USB card of the control computer.

The camera of the second imaging system 46 thus acquires a second image 52 of at least part of the second zone 34 around the spot for measuring ellipsometry at normal incidence.

A second image 52 is thus obtained which is clear over the entire field of the camera and without distortion of the area illuminated by the illumination beam 42 around the ellipsometry measurement spot.

However, the measurement spot 10 does not generally appear in the second image 52 unless the sample is sufficiently scattering.

Thus, the second imaging system 46 is generally not hampered by the reflection or the scattering of the incident measuring light beam 12.

Illumination beam 42 and second imaging beam 44 propagate along the normal to the sample and not along the oblique optical axis of the incident or reflected measurement light beam.

Consequently, the illumination beam 42 and the second imaging beam 44 in no way affect the ellipsometric measurements acquired via the detection system 26 of the ellipsometric signal.

Two separate images are thus available: on the one hand the first image 51 of the measurement spot under oblique incidence and on the other hand the second image 52 of the second zone 34 around the ellipsometric measurement spot under normal incidence.

These two images 51 and 52 are acquired by means of separate optical systems and cameras and generally have a different magnification from each other.

FIG. 5 illustrates an example of a first image 51 acquired on a reflecting sample in the reflection configuration with an angle of incidence of 70 degrees.

The dimensions of the measurement spot on the sample are approximately 1.2 mm in diameter not projected in circular shape (and 1.2 mm x 3.5 mm projected at 70 degrees in oval shape).

The dimensions of the spot are measured on a graduated sample or a staff.

In FIG. 5, a second spot 37 is observed formed by reflection of the measurement light beam on the rear face of the separator blade 27.

On the other hand, the first image 51 does not make it possible to visualize the patterns on the surface of the sample.

FIG. 6 illustrates an example of a second image 52 acquired under normal incidence on the sample 3 in the second zone 34 around the ellipsometry measurement spot.

The dimensions of the second area 34 imaged in image 52 of Figure 6 are approximately 4.2mm x 5.5mm.

In FIG. 6, the patterns on the surface of the sample are observed with excellent sharpness over the entire imaged area.

However, FIG. 6 does not make it possible to visualize the position or the dimensions of the ellipsometric measurement spot.

Let's go back to Figure 4.

The ellipsometer 100 further comprises an image processing system 10 5.

The image processing system 5 is connected by a first link 53 to the first imaging system 28 and by a second link 54 to the camera of the second imaging system 46.

The image processing system 5 receives in real time the first image 51 of the ellipsometric measurement spot and the second image 52 of the second zone 34 around the measurement spot.

The image processing system 5 is adapted to process the first image 51.

FIG. 7 illustrates a first image processing step in which the image processing system 5 is adapted to determine and extract a portion 55 of the first image 51 around the measurement spot 32.

The dimensions of the portion 55 depend on the size of the measurement spot.

The portion 55 corresponds to the central surface of the field of the camera where the spot 32 must be located.

By way of example, the portion 55 represents a rectangular area corresponding to approximately Nx = 400 ± 100 pixels horizontally by Ny = 265 ± 75 pixels vertically.

FIG. 8 schematically represents the image portion 55 of the measurement spot extracted from FIG. 7.

The image of the spot appears here almost circular.

FIG. 9 illustrates another image processing step applied to the image of the measurement spot of FIG. 8 in order to take therefrom an image of the contour 56 of the measurement spot.

For example, the color of the image 55 is changed by replacing the color of each black pixel by a transparent pixel except for the high intensity pixels greater than 1 which correspond to the shape of the measurement spot and which are unchanged.

Alternatively, those skilled in the art have other image processing techniques available to determine the image of the contour 56 of the measurement spot.

FIG. 10 illustrates another magnification and projection step applied to the image of the contour 56 of the measurement spot of FIG. 9 in order to deduce therefrom a projection 57 of the image of the measurement spot.

The magnification 5 applied corresponds to the magnification of the optical system between the actual size of the measurement spot on the sample and the dimension of the spot on the sensor of the camera 28.

By way of example, for a Uvisel Plus ellipsometer, the applied magnification factor is 1.54.

The magnification factor can be calibrated experimentally.

Depending on the relative orientation of the two cameras with respect to the orientation axes of the sample, it may be necessary to rotate the image of the spot, for example 90 degrees.

A projection coefficient is then applied in the X direction only so as to effect a projection of the measurement spot in the plane of the sample.

The applied projection coefficient is calculated as a function of the angle of incidence of the measurement beam on the sample.

This projection coefficient is calculated according to the geometric formula X = x (1 / cos (A01)).

For an angle of incidence of 70 degrees, the projection coefficient is approximately 2.92.

In other words, the image of the spot is enlarged by the projection coefficient 2.92 20 only along the projection axis, for example here the X axis.

The projection 57 of the image of the measurement spot corresponds to the measurement spot as it would appear in the second image 52 if the sample were scattering.

Thus, the spot 32 which appears on the camera 29 of circular shape, regains its real elliptical shape after stretching of the image.

Finally, the image processing system 5 combines the projection 57 of the image of the measurement spot with the second image 52 of the second zone 34 around the measurement spot to form a third image 58.

By way of non-limiting example, the combination of the images can be based on a step of superimposing or inlaying the projection 57 of the image of the measurement spot 30 on or in the second image 52 of the surface of the. sample at normal incidence.

The XY position of the projection in the 2nd image can be calibrated or adjusted beforehand, for example on a diffusing sample of the same thickness.

More precisely, we note the position of the center of the image of the measurement spot and its extent 4X, 4Y in the X, Y directions with respect to a reference pixel (0, 0) of the sample image.

It is possible to calibrate the XY position of the center of the measurement spot on the sample for different values of the angle of incidence, for example from 45 degrees to 80 degrees, in steps of 5 degrees.

The position of the image center of the measurement spot and its extent 4X, 4Y in the X, Y directions for different values of the angle of incidence are recorded in a table.

A polynomial of order two makes it possible to determine by interpolation the position of the center of the image of the measurement spot and its extent 4X, 4Y for the intermediate angle of incidence values.

FIG. 11 illustrates an example of a third image 58 obtained by superimposing or overlaying the projection of the image of the measurement spot (illustrated in FIG. 10) with the second image of the surface of the sample at normal incidence. .

This third image 58 is displayed on a display screen.

The user thus obtains a third image 58 which makes it possible to visualize simultaneously and with great clarity the patterns on the surface of the sample in an area around the measurement spot and the contours of the measurement spot projected onto the surface of the sample. sample.

The display of the third image can be very fast, for example less than 1 second after the acquisition and the processing of the first image 51 and of the second image 52.

The projection 57 of the image of the measurement spot corresponds to the measurement spot as it would appear in the second image 52 if the sample were scattering.

Images 51, 52 and 58 can be refreshed in real time.

This system makes it possible to position the measurement spot precisely with respect to the patterns on the surface of the sample, for example by moving the sample holder in the XY plane, without hindering the ellipsometric measurements.

This system makes it possible to visualize the position, the shape and the real dimensions of the measurement spot on the surface of the sample.

In particular, when a so-called multispot ellipsometer is used in which the dimensions of the measurement spot 30 are variable, for example from a source diaphragm forming a spot of transverse dimension ranging from 10 μm to a few hundred μm, the system allows the user to directly view and recognize the spot used.

In addition, an experienced user can roughly estimate and control the angle of incidence based on the apparent ellipticity of the projected measurement spot.

17 Optionally, the image processing system can include an image or pattern recognition module to identify and locate the pattern (s) where it is desired to position the measurement spot ellipsometry or else perform an autofocus adjustment on the sharpness of the image of the pattern.

In this way, it is possible to program ellipsometry measurements on a predetermined type of pattern and to position the measurement spot automatically on the selected pattern.

One application relates to the analysis of semiconductor or flat screen plates, in which patterns are repeated on the surface of the same substrate.

Automatic measurements with detection of the desired pattern, positioning of the measurement spot on the pattern concerned and acquisition of the measurement can thus be carried out.

FIG. 12 schematically represents various particular aspects of the imaging sub-assembly 4.

More particularly, according to one option, the imaging subassembly 4 comprises a spatial filter 47 disposed in the Fourier plane of the lens 45 of the camera 46.

The spatial filter 47 comprises for example a pinhole to reduce the geometric optical aberrations on the second image 52.

The imaging subassembly 4 can also include a plane mirror 40 for folding.

Advantageously, a near infrared filter 49 is disposed in front of the camera 46 to eliminate optical aberrations of the NIR wavelengths detected by the camera.

In FIG. 12, according to another particular and optional aspect, the imaging sub-assembly 4 further comprises a third optical beam splitter 61 arranged on the optical axis of the illumination beam 42 and another detection system 64.

The third optical beam splitter is chosen from the following components: glass plate or separator plate or semi with dielectric coatings or Polka-Dot plate or filter or splitter cube.

The third optical beam splitter is adapted to transmit a portion 65 of the light beam formed by reflection of the illumination beam 42 on the second area of the sample to the other detection system 64.

The other detection system 64 comprises for example a position detector with four quadrants.

In the example illustrated in FIG. 12, a diaphragm 62 and an optical system 63 are arranged between the third optical beam splitter 61 and the detection system 64.

The optical system 63 focuses the portion 65 of the light beam on the detection system 64.

This detection system 64 makes it possible to provide a signal representative of an angle 66 between the normal 31 to the surface of the sample 3 and the optical axis of the illumination beam 42.

As illustrated in FIG. 12, the sample holder 35 is provided with an actuator system 36 adapted to modify the angle of inclination of the sample holder transversely to the normal 31 to the surface of the sample.

By way of non-limiting example, the actuator system 36 is of the line-point-plane type and comprises two actuators and a pivot point, one of the two actuators operating a linear translation along the X axis and the axis. another actuator operating a linear translation along the Y axis around the pivot point.

An electronic system 6 is connected on the one hand to the other detection system 64 and on the other hand to the actuator system of the sample holder.

The electronic system 6 comprises for example an on-board electronic card.

The electronic system 6 receives the signal representative of the angle 66 between the normal 31 to the surface of the sample and the optical axis of the illumination beam 42 and applies a command to the actuator system 36 so as to reduce the angle of inclination 66 between the normal 31 to the surface of the sample and the optical axis of the illumination beam 42.

An adjustment of the sample holder in self-collimation with respect to the illumination beam 42 is thus obtained.

During a sample change, the imaging subassembly 4 thus makes it possible to quickly find the auto-animation setting without having to modify the alignment of the optical components of the ellipsometer.

According to another particular and optional aspect, the imaging sub-assembly 4 further comprises a polarizing optical device 67 arranged on the optical path of the illumination beam 42 and / or another polarizing optical device 68 arranged on the optical path of the imaging light beam 44.

More particularly, to make polarimetry measurements, a Glan type polarizer 67 is inserted on the illumination beam 42 and another Glan type polarizer 68 on the imaging light beam 44.

Alternatively, the splitter plate 43 and the polarizers 67, 68 are replaced by a single polarizer or a polarization splitter cube.

The imaging sub-assembly 4 thus forms a polarimeter under normal incidence.

Such a polarimeter makes it possible to study the variation in the state of polarization of the illumination beam 42 19 polarized by an anisotropic sample.

The incident illumination beam 42 is polarized, reflected by the sample and then analyzed by a polarizer 68 which acts as an analyzer upstream of the camera 46.

Preferably, the two polarizers 67 and 68 in polarization are oriented with crossed polarization axes so as to obtain an extinction of the imaging light beam 44 on an isotropic sample.

Thus, the polarimeter only detects the variations of state of polarization induced by reflection on an anisotropic sample.

The display system of the present disclosure can be factory installed on a new ellipsometer.

The present disclosure also proposes a display accessory intended to be installed on an existing ellipsometer.

This accessory comprises a first optical beam splitter 27 and a first imaging system 28, intended to be installed in the analysis section of the ellipsometer, an imaging sub-assembly 4 intended to be placed at normal incidence by relative to the sample to be analyzed and an image processing system 5.

The first imaging system 28 acquires a first image 51 under oblique incidence of a first zone 33 of the sample around the measurement spot, as described above, and transmits it to the image processing system 5.

The imaging sub-assembly 4 generates an illumination beam 42 intended to illuminate, under normal incidence 20, a second zone 34 of the sample around the measurement spot.

The imaging subassembly 4 acquires a second image 52 of the second area of the sample and transmits it to the image processing system 5.

The image processing system 5 applies a series of image processing steps to the first image and the second image to form a third image 58 comprising a projection of the image of the measurement spot onto the second image 52. of the sample, the projection 57 being adapted as a function of the angle of incidence of the incident light beam.

FIG. 13 schematically represents an ellipsometer mounted on a goniometer according to a particular embodiment.

Another type of instrument, reflectometer or polarimeter, can be installed on the goniometer in place of the ellipsometer.

The goniometer has a guide rail 70 of semicircular shape.

The excitation section 1 of the ellipsometer is mounted on an engine block 71 which allows the excitation section to be moved along the guide rail 70.

The center of rotation of the excitation section 1 during an excursion along the guide rail 70 is assumed to coincide with the ellipsometric measuring spot 32.

Symmetrically, the analysis section 2 of the ellipsometer is mounted on a motor unit 72 which allows the analysis section 2 to be moved along the guide rail 70 around the same center of rotation.

The analysis section 2 here comprises a first optical beam splitter 27 and a first imaging system 28, as described in connection with FIG. 4.

An imaging sub-assembly 4 is mounted on a plate fixed to the frame supporting the guide rail 70.

The imaging sub-assembly 4 here comprises the auxiliary source 41, the second imaging system 46, the four-quadrant detector 64 and the optical beam splitters 43 and 61 or a splitter cube (polarization or not) or polarizer.

The auxiliary source 41 emits the illumination beam 42 which is aligned with the normal 31 to the surface of the sample.

It can be seen clearly in FIG. 13 that the imaging sub-assembly 4 does not prevent the movements of the excitation section 1 and of the analysis section 2 in a wide range of angle of incidence for example. from 20 to 90 degrees.

Optionally, the imaging sub-assembly 4 can easily be removed to leave access, for example, for measurements at normal or near-normal incidence.

Those skilled in the art will easily adapt the reflection ellipsometer described in connection with FIGS. 4 and 13 to a transmission ellipsometer by simply moving the analysis section to place it on the optical path of the measurement light beam transmitted under incidence. oblique through a transparent sample.

On the other hand, those skilled in the art will easily adapt the ellipsometer described in connection with FIGS. 4 and 13 for polarimetric measurements.

Finally, by removing the polarization state analyzer from the analysis section and the polarizing device 14 from the excitation section 1, a simple reflectometer is easily obtained.

The measuring spot display system of the present disclosure is suitable for any type of measuring instrument of the reflectometer, polarimeter or ellipsometer type operating with an incident light beam for measuring under oblique incidence.

Method The present disclosure also relates to a method for measuring, reflectometry, ellipsometry or polarimetry comprising the following steps: emission of an incident light beam 12 intended to form a measuring spot on a sample 3 at an angle d oblique incidence; 5 - reception of a measuring light beam 22 formed by specular reflection or transmission of the incident light beam 12 on the sample 3; - optical separation of the measurement light beam 22 and transmission of a part of the measurement light beam to a first imaging system 28; acquisition by the first imaging system 28 of a first image 51 of a first zone 33 of the sample around the measurement spot; emission of an illumination beam 42 intended to illuminate at normal incidence a second zone 34 of the sample around the measurement spot; reception of an imaging light beam 44 formed by reflection of the illumination beam 42 on the second zone of the sample; optical separation of the illumination beam 42 and of the imaging light beam 44 and transmission of at least part of the imaging light beam 44 to a second imaging system 46; acquisition by the second imaging system 46 of a second image 52 of the second zone of the sample; - processing of the first image 51 adapted to extract an image from the measurement spot, resize and apply a projection to the image of the measurement spot as a function of the angle of incidence; and - generation of a third image comprising the projected and resized image of the measurement spot, the projected and resized image of the measurement spot being positioned and arranged in superposition or in incrustation in the second image 52 of said second zone of measurement. sample.

The visualization method described above is advantageously applied simultaneously with ellipsometric, polarimetric or reflectometry measurements under oblique incidence obtained from a detector 26 which receives a part of the measurement light beam other than that directed towards the first imaging system.

Claims (12)

CLAIMS 1. A measuring instrument (100) comprising an excitation section (1) and an analysis section (2), the excitation section (1) including a first light source (11) adapted to emit an incident light beam ( 12) for forming a measuring spot (32) on a sample (3) at an oblique angle of incidence, the analysis section (2) being arranged to receive a measuring light beam (22) formed by reflection or transmission of the incident light beam (12) on the sample (3), the analysis section (2) comprising a detection system (26) adapted to detect a part of the measurement light beam (22), characterized in that : - the analysis section (2) comprises a first optical beam splitter (27) and a first imaging system (28), the first optical beam splitter (27) being disposed on an optical path of the light beam of measurement (22) and able to transmit another part of the measurement light beam (22) to the first sy imaging system (28), the first imaging system (28) being adapted to acquire a first image (51) of a first area (33) of the sample around the measurement spot (32); and in that the measuring instrument further comprises: - a second light source (41) arranged so as to emit an illumination beam (42) intended to illuminate at almost normal incidence a second zone (34) of the sample around the measurement spot (32), a second imaging system (46) arranged to receive an imaging light beam (44) formed by reflection of the illumination beam (42) on the second area (34) of the sample and acquire a second image (52) of the second area (34) of the sample and - an image processing system (5) adapted to receive the first image (51) and the second image (52), the image processing system (5) being adapted to extract an image from the measuring spot of the first image (51) and to form a third image (58) comprising a projection (57) of the image. image of the measuring spot, the projection (57) being resized as a function of the angle of incidence of the incident light beam and said pr ojection being positioned and disposed in superposition or in incrustation in the second image (52) of the second zone of the sample. 24 2. A measuring instrument (100) according to claim 1 further comprising a second optical beam splitter (43) arranged to receive the illumination beam (42) from the second light source (41) and to direct the beam. illumination beam (42) to the sample (3), and the second optical beam splitter (43) being adapted to receive the imaging light beam (44) and direct it to the second imaging system (46). 3. Measuring instrument (100) according to claim 1 to 2 comprising at least one polarizing optical device (43, 68, 67) arranged on an optical path of the illumination beam (42) and / or of the imaging light beam. (44). 10 4. Measuring instrument (100) according to one of claims 1 to 3 wherein the second imaging system comprises a camera (46), an objective (45) and a spatial filter (47) arranged in an object focal plane. of the objective (45), the spatial filter (47) being adapted to reduce the optical aberrations on the second image (52). 15 5. Measuring instrument (100) according to one of claims 1 to 4 wherein the image processing system (5) comprises an image recognition subsystem suitable for delimiting a contour of the image of the spot. measurement in the first image (51) and / or to determine a first position and a first orientation of the first area of the sample in the first image (51) and / or, respectively to determine a second position and a second orientation of the second area of the sample in the second image (52). 6. A measuring instrument (100) according to claim 5 wherein the image recognition subsystem is adapted to automatically recognize at least one pattern in the second image (52). 7. A measuring instrument (100) according to claim 5 or 6 wherein the image recognition subsystem is adapted to recognize and select the image of the measurement spot (32) from among a plurality of images formed by reflection. multiples between two sides of the sample. 30 8. Measuring instrument (100) according to one of claims 1 to 7 further comprising a third optical beam splitter (61) and another detection system (64), the third optical beam splitter (61) being disposed. on the optical axis of the illumination beam (42), the third optical beam splitter being adapted to transmit a portion (65) of the light beam formed by reflection of the illumination beam (42) on the second region of the illumination beam (42). 'sample to the other detection system (64), the other detection system (64) being adapted to provide a signal representative of an angle (66) between the normal (31) to the surface of the sample ( 3) and an optical axis of the illumination beam 5 (42). 9. A measuring instrument (100) according to claim 8 comprising a sample holder (35) provided with an actuator system (36) adapted to modify at least one angle of inclination of the sample holder transversely to the normal ( 31) at the surface of the sample and an electronic system adapted to receive the signal representative of the angle (66) between the normal (31) at the surface of the sample and the optical axis of the illumination beam (42) and to apply a command to the actuator system (36). 10. The measuring instrument (100) according to one of claims 1 to 9 wherein the analysis section (2) comprising a polarization state analyzer (24) disposed on an optical path of the measuring light beam ( 22) and in which the detection system (26) is adapted to detect an ellipsometric or polarimetric signal. 11. Display accessory for a measuring instrument (100) based on the emission of an incident light beam (12) intended to form a measuring spot (32) on a sample (3) at an oblique angle of incidence and detecting a measuring light beam (22) formed by reflection or transmission of the incident light beam (12) on the sample (3), the measuring instrument (100) comprising a first imaging system (28) adapted to generate a first image (51) of a first area of the sample around the measurement spot (32), the first image (51) being formed by reflection or transmission of the incident light beam (12) on the sample, characterized in that the viewing accessory comprises: - a second light source (41) and a second imaging system (46), the second light source (41) being arranged to emit a beam illumination (42) intended to illuminate at almost normal incidence a second zone (34) of the sample around the measurement spot (32), the second imaging system (46) being arranged so as to form a second image (52) of the second zone (34) of the sample by reflection of the illumination beam ( 42) on the second zone (34) of the sample, and 26 - an image processing system (5) adapted to receive the first image (51) and the second image (52), the image processing system image (5) being adapted to extract an image from the measurement spot of the first image (51) and to form a third image (58) comprising a projection (57) of the image 5 of the measurement spot in superposition or in incrustation with the second image (52) of the sample, the projection (57) being resized according to the angle of incidence of the incident light beam (12). 12. A viewing accessory according to claim 11 further comprising a third optical beam splitter (61) and a further detection system (64), the third optical beam splitter (61) being disposed on the optical axis of the beam. illumination (42), the third optical beam splitter (61) being adapted to transmit a portion (65) of the light beam formed by reflection of the illumination beam (42) on the second region (34) of the sample to the other detection system (64), the other detection system (64) being adapted to provide a signal representative of an angle (66) between the normal (31) to the surface of the sample (3) ) and an optical axis of the illumination beam (42).